Figures for maximum crop growth rates, reviewed by Gifford (1974), suggest that the productivity of C3 and C4 species is almost indistinguishable. However, close inspection of these figures at source and correspondence with several authors revealed a number of errors. When all unreliable figures were discarded, the maximum growth rate for C3 stands fell in the range 34–39 g m−2 d−1 compared with 50–54 g m−2 d−1 for C4 stands. Maximum growth rates averaged over the whole growing season showed a similar difference: 13 g m−2 d−1 for C3 and 22 g m−2 d−1 for C4. These figures correspond to photosynthetic efficiencies of approximately 1·4 and 2·0%.

Experiments with farmers' traditional practice of growing cereals with groundnuts demonstrated that the system consistently produced greater cash returns than sole-crop groundnuts. Increasing the proportion of cereal, and incorporating maize in addition to sorghum and millet, increased cash returns even further.

Responses in yield of dry bean genotypes of different growth habits [determinate (Type I), indeterminate small vine (Type II), indeterminate large vine (Type III), and indeterminate climbing (Type IV)] were evaluated over two growing seasons. Types II and III gave higher yields than Type I, with Type II the highest. Narrow between-row spacings (50 cm) tended to give higher yields than 75 cm spacings for all habits, though Type I seemed less responsive than the indeterminate habits, Types II and III. Close within-row spacing (5 versus 10 cm) was not beneficial for beans of any growth habit. Yields of beans with climbing habit grown on different support systems and at different spacings are also reported.

Two different collections of local sorghum strains, grown in 1975/76 and 1976/77, showed considerable and useful variation in plant height at maturity, head type and exsertion, grain colour, and days to flowering and maturity. A close and positive correlation was found between days to flowering and to maturity, and x2 tests also showed close associations among other characters. Implications of these variabilities for sorghum improvement are briefly discussed.

A glasshouse was built over an established tea crop in Malawi, and the internal air temperature was controlled by manual regulation of the heating, cooling and ventilation rates of two domestic air conditioners. When the inside environment was carefully matched to conditions outside, the glasshouse had only a minor influence on the tissue temperature, stomatal behaviour, leaf water potential and shoot growth of the bushes. The system could be a useful aid to experimentation on the temperature and water relations of field crops in the tropics.

Colour development in fruits of dark purple eggplant cultivars was greatly influenced by temperature conditions. During the cool season, colour development was much slower than during the hot season, corresponding to slower fruit growth and much lower final weight. There were varietal differences in seasonal influence on the distribution of various colour shades, both during fruit growth and at harvest. Soil heating during the cool season improved fruit colour.

The effects on local cucumbers of supplementary mineral fertilizers over an initial field dressing of 30 tonnes of poultry manure and 4 tonnes of lime/ha, were determined on tropical peat soil in Brunei. Significant yield increases were obtained with supplementary N up to 280 kg/ha but not with K/Mg above the basal rates 78/10 kg/ha. The highest yields exceeded 50 tonnes/ha of marketable fruit, obtained over a 9-week growing period.

Two experiments to investigate the micronutrient requirements of cassava (cv Black Twig) on Malaysian peat soil are described. Cu was found to be the only essential micronutrient and Mn, Zn, Fe, Mo and B were not needed. Fertilizing with 20 kg/ha of copper sulphate approximately tripled tuber dry matter, and starch and Cu uptake, but applying 10 kg/ha of copper sulphate gave the same results. Each crop of cassava absorbed only about 2% of the applied Cu, giving a leaf Cu content of about 14 ppm compared with about 7 ppm in Cu-deficient plants. Cu deficiency symptoms were invariably observed in Cu-deficient plots and these are also described.

Fourteen varieties of cowpea (Vigna unguiculata (L.) Walp.) were compared for yields of forage and seed from two sowing dates, using various agronomic parameters. Yields ranged from 1048 to 5044, 185 to 920 and 864 to 3321 kg/ha for dry matter, crude protein and seed respectively, with advantages from spreading as against semi-erect types, and early rather than late July sowing. IVu 1283-1 and IVu 1283-2 effectively combined vegetative and seed yield, and appeared most suitable for fodder and seed production. A simple forage yield index (FYI), useful in yield prediction, was evolved.

A 4-year investigation of the effects of sowing date on three types of groundnut showed that the earlier the sowing date, the later was kernel initiation and kernel maturity. Early sowing resulted in a high pod yield, oil content and iodine number, but reduced the shelling percentage. The leaf area index ranged from 3·0 to 5·0, the highest value being obtained with early sowing and with non-upright bunch varieties.

Water use efficiency of maize (Zea mays) and cowpea (Vigna unguiculata) was investigated, with and without tillage, under four irrigation frequencies in which 12 mm of water was applied at 2, 4, 8 and 12 day intervals, using a sprinkler system. Both maize and cowpea under no-tillage yielded more than with conventional ploughing. Water use efficiency of maize without tillage was 18·3, 17·5, 57·8 and 100% greater than with tillage at irrigation frequencies of 2, 4, 8 and 12 days respectively. Whereas the leaf water potential of cowpea was not affected by tillage, that of maize was generally higher for no-tillage compared with conventional ploughing.

The yield of Chipewa variety of soyabean was investigated in relation to spacing and fertilizer levels on a range of paddy soils exhibiting good, medium and poor drainage. Under good conditions of drainage optimum yield was obtained at a density of 100,000 plants/ha and a fertilizer level equivalent to N—54, P2O5—54, K2O—75 and MgO—9 kg/ha. Under poorer conditions of drainage yield continued to increase up to a density of 162,000 plants and fertilizer levels of twice the above rates. Even under sub-optimal drainage conditions, however, satisfactory yields equivalent to about 1500 kg/ha were obtained from this variety.

Maize and cowpea were grown in mixed and pure stands, using the same overall density in all plots. Four fertilizer treatments N0P0, N1P0, N0P1 and N1P1 were imposed in experiments carried out during the early growing seasons of 1976 and 1977 at Ibadan in the rainforest zone of Nigeria. There was no competition between the crops for nitrogen or phosphorus and yields in mixtures were significantly higher than the means of the species monocultures, as shown by relative yield total (RYT) and C (complementation) values.

The conventional method of inoculating Phaseolus vulgaris with Rhizobium phaseoli, using a peat carrier and dry seeds, was compared with a method using a slurry inoculation of germinating seeds, which were subsequently sown with a fluid drill. The mean number of nodules per plant 28 days after sowing was 0·64 (uninoculated control), 2·14 (dry seed), and 7·0 (fluid drill), differences between treatments being significant at P=0·01. Two varieties included in the experiment gave similar responses, and it is concluded that the fluid drill technique has a useful potential as a method of ensuring good inoculation of legume seedlings.

Measurements of the stomatal apertures of young clonal tea plants (Camellia sinensis) showed that stomata of plants irrigated during the dry seasons only were wider open than those not irrigated during both wet and dry seasons. Similarly, xylem water potential values (ψx) were always higher (less negative) in irrigated than non-irrigated plants, during both wet and dry seasons. The results suggest that more drought-susceptible clones have a greater demand for water than those less susceptible to drought.

Effects of Alar on growth, flowering and yield parameters of standard-planted and closely-planted late-bearing okra were studied. Lower concentrations of Alar, applied once 6 weeks after sowing on standard-planted okra, significantly advanced days to first flowering and depressed height at first flowering and final height. Higher Alar concentrations, particularly 2000 ppm applied twice after 3 and 6 weeks on closely-planted okra, produced more, longer and heavier pods, and therefore higher total pod yield in unstopped than in stopped okra, in addition to advancing days to first flowering and depressing height at first flowering and final height. The agronomic practice of stopping okra at 6 weeks reduced pod number, pod weight/plant and total pod yield/ha in unsprayed plants.

Combined effects of nitrogen at 25 and 50 kg/ha as calcium ammonium nitrate and phosphorus at 30, 60 and 90 kg/ha as triple superphosphate were studied on the composition, germination and emergence of sunflower seeds. Maximum protein (26·2%) and lipid (45·8%) with the maximum emergence (85·0%) was obtained from seeds produced by crops raised in soil with 50 kg/ha of nitrogen and 60 kg/ha of phosphorus. Lowest protein (21·6%), lipid (40·8%) and 45·0% emergence were obtained from seeds of crops raised on soil with the basal level of nitrogen and phosphorus.

Optimum conditions are described for the in vivo measurement of nitrate reductase activity in field-grown cotton leaves. The incubation period depended on light conditions prior to sampling. Addition of 1 mM glycolate had the effect of increasing apparent nitrate reductase activity on most days tested, and followed the general rhythmical pattern exhibited by the enzyme assayed without glycolate. While the in vivo assay appears to correlate well with soil nitrate levels, the choice of assay conditions does not appear to be absolutely critical.

Broadsense heritability, and correlations of grain yield and related characters, were estimated in three crosses under two levels of soil fertility, which profoundly affected heritability of height and seed weight. Grain yield exhibited heritability of 51–81%, and in one cross significant heterosis in F2. Amongst yield-related characters only pods/plant and seeds/pod were both correlated to yield, and also lacked negative genotypic correlations with other economic characters. However, direct selection for grain yield was considered more efficient than indirect selection using yield-related characters.

Clearing cotton stalks after picking is enforced by law in the Sudan to stop the spread of black-arm and leaf curl diseases. The magnitude of pull and lift requirements to uproot a single plant are important parameters in designing an efficient stalk-pulling machine. With the help of a specially built apparatus, 186 plants selected at random were uprooted and measurements of the magnitude of pull and plant lift were recorded. A magnitude of 121 kg pull, accompanied by a short lift of 4·9 cm, were found necessary to loosen all plants completely. Investigations have also included the percentage of plants pulled and their root dimensions in relation to the yield point.